As an important aspect of optical communications, the modulation and switching especially of near-infrared radiation has received considerable attention; of particular current importance is the modulation of such radiation by means of an electrical signal. Modulation may take the form of direct intensity modulation of a light source; alternatively, means are desired for indirect modulation, e.g., as applied to radiation from a source having essentially constant intensity. One such indirect modulation device, disclosed by C. J. Chang-Hasnain et al., "Tunable Electroabsorption in Gallium Arsenide Doping Superlattices", Applied Physics Letters, Vol. 50 (1987), pp. 915-917, is based on the use of a superlattice of gallium arsenide semiconductor layers which, in groups of four, are n-doped, intrinsic, p-doped, and intrinsic. The invention as disclosed below is motivated by the desire for providing a semiconductor modulator device having improved absorption characteristics as well as enhanced bias capability.
Further considered as relevant with respect to the invention are the papers by E. F. Schubert et al.,
[1] "Radiative Electron-Hole Recombination in a New Sawtooth Semiconductor Superlattice Grown by Molecular-beam Epitaxy", Physical Review B, Vol. 32 (1985), pp. 1085-1089, PA1 [2] "The Delta-doped Field-effect Transistor (.delta.FET)", IEEE Transactions of Electron Devices, Vol. ED-33 (1986), pp. 625-632, and PA1 [3] "Spatial Localization of Impurities in Delta-doped n-type GaAs", Applied Physics Letters, Vol. 52 (1988), pp. 1508-1510.